1. Field of the Invention
The invention relates to a structure and a method for adjusting the rotational balance of a rotational-part assembly consisting of a plurality of parts including a crankshaft and a damper pulley in an engine having an engine body on which the damper pulley is mounted together with other parts.
2. Description of the Related Art
An engine body mounted in a motor vehicle, or the like, includes pistons that are disposed in cylinders formed in the cylinder body such that the pistons can reciprocate therein. The pistons are connected to the crankshaft, which is the output shaft of the engine, via connecting rods. The cylinder head is provided on the upper end of the cylinder block, and combustion chambers are defined between the cylinder head and the respective pistons. The pistons reciprocate as air-fuel mixtures are combusted in the combustion chambers, and the reciprocation of the pistons turns the crankshaft via the connecting rods.
Various parts are mounted on the engine body, such as a damper pulley attached to the front end of the crankshaft and a flywheel attached to the rear end of the crankshaft. In this specification, an assembly obtained by mounting such parts including the damper pulley and the flywheel to the engine body will be referred to as “engine assembly”.
Among the parts mounted on the engine body, the damper pulley is a pulley that has a damping function, as well as the function for transmitting the rotational force from the crankshaft to auxiliaries, such as those in a motor vehicle (e.g., compressor for air-conditioner, power steering pump). For example, Japanese Patent Application Publication No. 63-246564 (JP-A-63-246564) describes the aforementioned technology.
An example of a damper pulley is shown in FIG. 13. The damper pulley 402 of this example has a cylindrical hub 421 that is connected to a crankshaft 150 via arms 425 and a boss 424, a damper rubber 423 provided on the outer periphery of the hub 421, a cylindrical damper mass 422 provided on the outer periphery of the damper rubber 423. According to this structure, when the crankshaft 150 is rotating, the hub 421 and the damper mass 422 resonate with the damper rubber 423 interposed therebetween and this resonation cancels the torsional vibration of the crankshaft 150, so that the vibration of the crankshaft 150 is damped. Also, in this damper pulley 402, V-grooves 422a are formed in the outer surface of the damper mass 422 and the belt for driving the auxiliaries, such as the air conditioner compressor and the power steering pump, is wound around the damper pulley 402 by being fit on the V-grooves 422a. 
Typically, the rotational balance of a rotational-part assembly consisting of a plurality of parts that are mounted on the engine body (e.g., damper pulley, flywheel, crankshaft) is adjusted by adjusting the rotational balance of each part. Therefore, to obtain a desired rotational balance of the engine assembly, the rotational balance of each part needs to be finely adjusted. Also, even if a desired rotational balance of each part constituting the rotational-part assembly can be obtained, the rotation of the rotational-part assembly mounted on the engine assembly may be out of balance due to, for example, the tolerances for attaching the respective parts to the crankshaft.